1. Field of the Invention
The invention relates in general to an image capturing apparatus, which can do one pass duplex image scanning, and its method, and more particularly to an image capturing apparatus and method, which can reduce the period of time in waiting for image data in buffer memories to be transmitted before the next document can be scanned and improve the scan efficiency.
2. Description of the Related Art
Today's technology places emphasis on speed and efficiency. Hence, scanners are constantly innovated in order to increase the scan speed in addition to providing high-quality images by resolution improvement. For example, flatbed scanners in early years took a lot of time reading images, for documents can only be manually placed on the flatbed and be scanned sheet by sheet. After the automatic document feeding technique has been developed, the scanner equipped with the automatic document feeder (ADF) can continuously scan tens of sheets of documents and transmit the image data thereof to computers for further processing, thereby saving the time of placing and retrieving each of the documents manually. Some scanners with automatic document feeding function can even read documents by one pass duplex scanning.
Referring to FIG. 1A, a lateral view of a flatbed image capturing apparatus, which is equipped with an ADF to perform one pass duplex scanning, is shown. The image capturing apparatus 100 includes a base 110, and an ADF 120 disposed on the base 110. The ADF 120 is provided for feeding to-be-scanned documents 122, and each document 122 has a first page of data 122a (the page facing upward) and a second page of data 122b (the page facing downward). The base 110 includes a flatbed 112, a first image sensor 114, and a circuit board 116, while the ADF 120 includes a second image sensor 124. As the documents 122 are to be scanned, they are fed onto the flatbed 112 via the ADF 120, in which the first page of data 122a and the second page of data 122b of each document are respectively read by the first image sensor 114 installed in the base 110 and the second image sensor 124 installed in the ADF 120. The image data thereof are converted to electrical signals and stored in memories on the circuit board 116, or further transmitted to an exterior host 130. FIG. 1B shows a lateral view of a one-pass-duplex-scanning sheet-fed scanner. Its process of one pass duplex scanning is similar to that of the flatbed scanner having the ADF as shown in FIG. 1A.
Referring to FIG. 1C, a block diagram illustrating the image reading of the image sensors, and the storage and transmission of the corresponding image data in FIG. 1A and FIG. 1B is shown. The circuit board 116 includes a memory module 117 and an image processor 118. The memory module 117 includes a first memory (buffer memory) 117a and a second memory (buffer memory) 117b for respectively registering the image data I112a, corresponding to the first page of data 122a and read by the first image sensor 114, and the image data I122b, corresponding to the second page of data 122b and read by the second sensor 124. The image processor 118 is provided for processing the image data transmitted from the memory module 117 and transmitting them to the host 130.
Generally, the image data I122b can be transmitted to the memory module 117 only after the image data I122a, previously stored in the memory module 117, has been transmitted to the image processor 118. For scanners having a high resolution of, for instance, 600 dpi, the speed of the image sensors 114 and 124 reading documents 122 is usually higher than that of transmitting image data I122a and I122b from the memory module 117 to the image processor 118. That is, the scan time (ts) is usually smaller than the data transmission time (td) as shown in FIG. 1D. Supposed that T1 is the time of performing one pass duplex scanning of one sheet of document 122, and T1a and T1b are respectively the time of transmitting the corresponding image data I122a and I122b from the memory module 117 to the image processor 118, both T1a and T1b are larger than T1. Therefore, the image data I122a and I122b corresponding to a certain sheet of document 122 can only be registered in the memory module 117 after those corresponding to the prior sheet of document 122 are being completely transmitted. This period of delay time Tw is (T1a+T1b−T1). The delay time Tw recurs and adds up as each sheet of document 122 is being scanned, so the more documents are being scanned, longer the period of the delay time will be in the scanning process. As a result, the scan speed and scan efficiency will be greatly reduced.